This invention relates generally to cryogenic air separation and is particularly useful for enhancing the ability of a cryogenic air separation system to produce liquid product.
A cryogenic air separation plant has fixed refrigeration output and liquid product rates based on existing equipment. Increases in liquid production are frequently required beyond existing system capabilities. Such increases may be achieved by reconfiguring the existing system by using the main heat exchanger to supply the requisite additional refrigeration. However, such a reconfiguration to existing equipment is difficult and costly to implement.
Accordingly it is an object of this invention to provide a cryogenic air separation system having enhanced liquid capacity wherein the requisite additional refrigeration is provided to the cryogenic air separation plant without involving the main heat exchanger.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for carrying out cryogenic air separation comprising:
(A) compressing feed air and passing a first portion of the compressed feed air into a cryogenic air separation plant;
(B) further compressing a second portion of the compressed feed air to produce further compressed feed air, turboexpanding a first part of the further compressed feed air and warming the turboexpanded first part of the further compressed feed air by indirect heat exchange with a second part of the further compressed feed air to condense said second part of the further compressed feed air;
(C) passing the condensed second part of the further compressed feed air into the cryogenic air separation plant; and
(D) producing by cryogenic rectification within the cryogenic air separation plant at least one of product oxygen, product nitrogen and product argon.
Another aspect of the invention is:
Apparatus for carrying out cryogenic air separation comprising:
(A) a primary compressor, a booster compressor, a cryogenic air separation plant, means for passing feed air to the primary compressor, means for passing feed air from the primary compressor to the cryogenic air separation plant, and means for passing feed air from the primary compressor to the booster compressor;
(B) a turboexpander, a heat exchanger having a cooling pass and a warming pass, means for passing feed air from the booster compressor to the turboexpander and from the turboexpander to the warming pass, and means for passing feed air from the booster compressor to the cooling pass;
(C) means for passing feed air from the cooling pass to the cryogenic air separation plant; and
(D) means for recovering at least one of product oxygen, product nitrogen and product argon from the cryogenic air separation plant.
As used herein the term xe2x80x9cfeed airxe2x80x9d means a mixture comprising primarily oxygen, nitrogen and argon, such as ambient air.
As used herein the term xe2x80x9ccolumnxe2x80x9d means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. The term xe2x80x9cdouble columnxe2x80x9d is used to mean a higher pressure column having its upper end in heat exchange relation with the lower end of a lower pressure column.
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases is generally adiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the terms xe2x80x9cturboexpansionxe2x80x9d and xe2x80x9cturboexpanderxe2x80x9d mean respectively method and apparatus for the flow of high pressure gas through a turbine to reduce the pressure and the temperature of the gas, thereby generating refrigeration.
As used herein the term xe2x80x9ccompressorxe2x80x9d means a machine that increases the pressure of a gas by the application of work.
As used herein the term xe2x80x9ccryogenic air separation plantxe2x80x9d means a facility for fractionally distilling feed air, comprising one or more columns and the piping, valving and heat exchange equipment attendant thereto.
As used herein the term xe2x80x9cbooster compressorxe2x80x9d means a compressor which provides additional compression for purposes of attaining higher air pressures required for the condensation of feed air.
As used herein the term xe2x80x9cproduct oxygenxe2x80x9d means a fluid having an oxygen concentration of at least 90 mole percent.
As used herein the term xe2x80x9cproduct nitrogenxe2x80x9d means a fluid having a nitrogen concentration of at least 99 mole percent.
As used herein the term xe2x80x9cproduct argonxe2x80x9d means a fluid having an argon concentration of at least 97 mole percent.